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1
12-03-2017
Dr Abhishek.S (R2)
Radiographics Dept of Radio-diagnosis
KODAK
GOVERNMENT MEDICAL COLLEGE
BARODA
For nearly 100 years
Conventional photographic films
Storage phosphor based Computed radiography
(CR).
DISADV –Requiring read out & processing mechanisms.
Digital Radiography
flat panel detectors with integrated
readout mechanism.
2
The excitement surrounding DR is
1.Rapid access to digital images wherever
stationary x-rays are taken.
2.Provides image quality that exceeds both
conventional and CR.
3
 Basic overview
X-RAY EXPOSURE
DETECTORS
IMAGE PROCESSING
DISPLAY
4
Functional components:
 A digital image receptor
 A digital image processing unit
 An image management system
 Image and data storage devices
 A communications network
 A display device.
5
6
7
8
Receptor consists of matrix of
many
Individual pixel elements.
9
Digital Radiography Detector
Technologies
 CCD* Camera - Indirect
 Flat Panel – Indirect
 Flat Panel - Direct
10
11
12
13
Scintillator / CCD Camera
Lens minification:
• small collection angle
• poor light collection efficiency
• loss of signal-to-noise
• image distortion
Collection angle
Image Minification
High DQE
CCD Sensor
High DQE
Scintillator
Poor light collection efficiency
14
Scintillator / CCD Camera
CCD - Charge Coupled
Device
Photo-diode elements
sensitive to light
small surface area (< 16
cm2
)
small pixel size (< 25
microns)
15
Scintillator / CCD Camera Limitations
Readily available
components
Low investment
Potential rapid imaging
Multiple Lenses & Mirrors
large minification, distortion,
image stitching
Fiber-optic Tapers
limited minification, distortion,
light loss
Complex image processing
Mechanical complexity
Strengths Weaknesses
16
Computer Displays
Flat Panel Technology
Amorphous Silicon
Active Matrix
Flat-panel digital radiographic x-ray detectors can
be divided into two classes:
 Direct conversion detectors
which x-ray energy is converted directly into
electric charge.
o Indirect conversion detectors,
in which x-ray energy is first converted to light
by an x-ray scintillllator.
17
18
Flat Panel Detectors
Direct
TFT array
Semiconductor
Signal
profile
Indirect Xray
quantum
Signal
profile
Scintillator
Layer
Xray
quantum
-0.50 -0.25 0 0.25 0.50
Distance (mm)
-0.50 -0.25 0 0.25 0.50
Distance (mm)
TFT/TFD
array
19
Scintillator
Absorbed
X Ray Quantum
Unabsorbed
X Ray Quantum
GdOS
or
CsI
The two most common scintillators are
cesium iodide
gadolinium oxysulfide.
20
21
Flat Panel Detectors
Direct
TFT array
Semiconductor
Signal
profile
Indirect Xray
quantum
Signal
profile
Scintillator
Layer
Xray
quantum
-0.50 -0.25 0 0.25 0.50
Distance (mm)
-0.50 -0.25 0 0.25 0.50
Distance (mm)
TFT/TFD
array
22
Flat Panel DetectorsFlat Panel Detectors
x-raysx-rays ⇒⇒ lightlight ⇒⇒ chargecharge
scintillatorsscintillators
powder (GdOS)powder (GdOS)
structured (CsI)structured (CsI)
photodiode on TFTphotodiode on TFT
Drivers:Drivers:
High absorption (CsI)High absorption (CsI)
Dynamic imagingDynamic imaging
x-raysx-rays ⇒⇒ chargecharge
x-ray photoconductorx-ray photoconductor
SeleniumSelenium
Standard TFTStandard TFT
Drivers:Drivers:
Low costLow cost
High resolutionHigh resolution
Indirect Direct
superior image quality over film/screen and CR systems
static and dynamic imaging capabilities
23
Flat Panel DetectorsFlat Panel Detectors
24
Photodiode or
Storage Capacitor
Data Line
Gate Line
TFT Switch aSi
Flat Panel Detectors – TFT DetailFlat Panel Detectors – TFT Detail
25
Scintillator - Cesium IodideScintillator - Cesium Iodide
0
0.2
0.4
0.6
0.8
1.0
0 1 2 3 4 5
CsI (600µm)
GdOS (167µm)
Spatial Frequency (mm
-1
)
ModulationTransferFactor
26
27
200 µm
400 µm
Scintillator / Flat PanelScintillator / Flat Panel
DetectorDetector
Effective Pixel Size
-0.50 -0.25 0 0.25 0.50
Line Spread Function:
Equivalent
Aperture = 400µm
200 µm Pixel Size
Distance (mm)
Effective Pixel Size
Actual Pixel Size
CsI Light Spread
28
Scintillator / Flat Panel
Detector
 CsI - high x-ray
absorption.
 High DQE
 Low scatter
sensitivity.
 Advantaged at high
kV.
 Dynamic / rapid
imaging.
 High manufacturing
cost.
 Dedicated TFT line
required.
 GdOS lower DQE.
 CsI is hygroscopic.
Strengths Weaknesses
29
Scintillator / Flat PanelScintillator / Flat Panel
DetectorDetector
30
Photoconductor / Flat
Panel Detector
Drawing not to scale
Programmable
high-voltage
power supply
X-rays
Gate
pulse
Charge amplifier
Thin-film transistor
Signal storage
capacitor
Glass substrate
Charge collection
electrode
Electron blocking layer
X-ray semiconductor
Dielectric
layer
Top electrode
Selenium
E
31
Photoconductor / FlatPhotoconductor / Flat
Panel DetectorPanel Detector
Kodak DirectView Detector
Magnified view of a portion of the TFTMagnified view of a portion of the TFT
matrix. Arrow points to the center of amatrix. Arrow points to the center of a
single 139 µm detector elementsingle 139 µm detector element
DR9000
32
Why Selenium asWhy Selenium as
Photoconductor?Photoconductor?
♦ Intrinsic high spatial
resolution
♦ Demonstrated across
the full medical
diagnostic range
(mammography through
chest)
♦ Dynamic image
capabilities .
♦ Long life
♦ Can be uniformly
deposited over a large
area
♦ Best advantage used in
“charge accumulation
mode”
33
Photoconductor / Flat PanelPhotoconductor / Flat Panel
DetectorDetector
-0.50 -0.25 0 0.25 0.50
Line Spread Function
Equivalent
Aperture = 139µm
139µm Pixel Size
Distance (mm)
139µm
139µm
Effective Pixel Size
Actual Pixel Size
34
-0.50 -0.25 0 0.25 0.50
Distance (mm)
Light spread and loss ofLight spread and loss of
sharpnesssharpness
35
0
0.2
0.4
0.6
0.8
1.0
0 1 2 3
Film-Screen
CCD
Computed
Radiography
Direct Conversion
Detector
Indirect Conversion
Detectors
Spatial frequency (mm
-1
)
ModulationTransferFactor
36
Photoconductor / Flat PanelPhotoconductor / Flat Panel
DetectorDetector
 Low manufacturingLow manufacturing
cost.cost.
 DQE > CR & CCDDQE > CR & CCD
 Advantaged at lowAdvantaged at low
kV (mammography)kV (mammography)
 Se - low x-raySe - low x-ray
absorptionabsorption
 DQE < Indirect/CsIDQE < Indirect/CsI
 High scatterHigh scatter
sensitivitysensitivity
 Image lag effects.Image lag effects.
 Thermal sensitivity.Thermal sensitivity.
Strengths Weaknesses
37
There are two types of images, analog and digital, used in
medical imaging.
 Analog imagesAnalog images are the type of images that we, as
humans, look at.
 They include such things as TV images and all of our medical
images displayed on various display devices, like computer
monitors.
 Digital imagesDigital images are recorded as numbers for the computer
systems.
38
39
40
 A digital image is represented in the imaging and
computer system by numbers in the form of binary
digits, called bits.
 Then, multiple bits represent a Pixel.
 Then matrix of pixels represent the Digital image.
41
42
 The pixel bit depth is the number of bits that
have been made available in the digital system to
represent each pixel in the image.
43
44
 When the pixel bit depth is increased to eight
bits, a pixel can then have 256 different values
(brightness levels, shades of gray, etc).
45
46
47
 When an image is in digital form, it is actually
blurred by the size of the pixel.This is because all
anatomical detail within an individual pixel is
"blurred together" and represented by one
number.
 The physical size of a pixel, relative to the
anatomical objects, is the amount of blurring
added to the imaging process by the digitizing of
the image.
 An image with small pixels (less blurring) displays
much more detail than an image made up of larger
pixels.
48
49
 There are several digital processing methods
that can be used to adjust the contrast
characteristics of an image.
 The two methods that we will consider here
are:
1. Look Up Table (LUT) processing
2. Windowing
50
51
52
 Many radiologists find value in having an .
inverted (black bone) image in addition to the
conventional (white bone) image at the time of
viewing.
 Some objects and structures might be more
visible and easier to detect on the inverted
image.
53
54
55
 The process consist of two distinct steps. First,
a blurred copy of the original image is
produced.
 by replacing each pixel value with the average
of the pixel values in it's neighborhood.
 This produces a "blurred mask" image
56
 The final step is where the computer subtracts the
blurred mask image (actually some fraction of it)
from the original image.
 This process increases the contrast of the details.
 The result is that the contrast and visibility of the
detail (small objects and structures) in enhanced.
57
58
59
THANK YOU
60

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Dr,system abhishek

  • 1. 1 12-03-2017 Dr Abhishek.S (R2) Radiographics Dept of Radio-diagnosis KODAK GOVERNMENT MEDICAL COLLEGE BARODA
  • 2. For nearly 100 years Conventional photographic films Storage phosphor based Computed radiography (CR). DISADV –Requiring read out & processing mechanisms. Digital Radiography flat panel detectors with integrated readout mechanism. 2
  • 3. The excitement surrounding DR is 1.Rapid access to digital images wherever stationary x-rays are taken. 2.Provides image quality that exceeds both conventional and CR. 3
  • 4.  Basic overview X-RAY EXPOSURE DETECTORS IMAGE PROCESSING DISPLAY 4
  • 5. Functional components:  A digital image receptor  A digital image processing unit  An image management system  Image and data storage devices  A communications network  A display device. 5
  • 6. 6
  • 7. 7
  • 8. 8 Receptor consists of matrix of many Individual pixel elements.
  • 9. 9
  • 10. Digital Radiography Detector Technologies  CCD* Camera - Indirect  Flat Panel – Indirect  Flat Panel - Direct 10
  • 11. 11
  • 12. 12
  • 13. 13 Scintillator / CCD Camera Lens minification: • small collection angle • poor light collection efficiency • loss of signal-to-noise • image distortion Collection angle Image Minification High DQE CCD Sensor High DQE Scintillator Poor light collection efficiency
  • 14. 14 Scintillator / CCD Camera CCD - Charge Coupled Device Photo-diode elements sensitive to light small surface area (< 16 cm2 ) small pixel size (< 25 microns)
  • 15. 15 Scintillator / CCD Camera Limitations Readily available components Low investment Potential rapid imaging Multiple Lenses & Mirrors large minification, distortion, image stitching Fiber-optic Tapers limited minification, distortion, light loss Complex image processing Mechanical complexity Strengths Weaknesses
  • 16. 16 Computer Displays Flat Panel Technology Amorphous Silicon Active Matrix
  • 17. Flat-panel digital radiographic x-ray detectors can be divided into two classes:  Direct conversion detectors which x-ray energy is converted directly into electric charge. o Indirect conversion detectors, in which x-ray energy is first converted to light by an x-ray scintillllator. 17
  • 18. 18 Flat Panel Detectors Direct TFT array Semiconductor Signal profile Indirect Xray quantum Signal profile Scintillator Layer Xray quantum -0.50 -0.25 0 0.25 0.50 Distance (mm) -0.50 -0.25 0 0.25 0.50 Distance (mm) TFT/TFD array
  • 20. The two most common scintillators are cesium iodide gadolinium oxysulfide. 20
  • 21. 21 Flat Panel Detectors Direct TFT array Semiconductor Signal profile Indirect Xray quantum Signal profile Scintillator Layer Xray quantum -0.50 -0.25 0 0.25 0.50 Distance (mm) -0.50 -0.25 0 0.25 0.50 Distance (mm) TFT/TFD array
  • 22. 22 Flat Panel DetectorsFlat Panel Detectors x-raysx-rays ⇒⇒ lightlight ⇒⇒ chargecharge scintillatorsscintillators powder (GdOS)powder (GdOS) structured (CsI)structured (CsI) photodiode on TFTphotodiode on TFT Drivers:Drivers: High absorption (CsI)High absorption (CsI) Dynamic imagingDynamic imaging x-raysx-rays ⇒⇒ chargecharge x-ray photoconductorx-ray photoconductor SeleniumSelenium Standard TFTStandard TFT Drivers:Drivers: Low costLow cost High resolutionHigh resolution Indirect Direct superior image quality over film/screen and CR systems static and dynamic imaging capabilities
  • 23. 23 Flat Panel DetectorsFlat Panel Detectors
  • 24. 24 Photodiode or Storage Capacitor Data Line Gate Line TFT Switch aSi Flat Panel Detectors – TFT DetailFlat Panel Detectors – TFT Detail
  • 25. 25 Scintillator - Cesium IodideScintillator - Cesium Iodide 0 0.2 0.4 0.6 0.8 1.0 0 1 2 3 4 5 CsI (600µm) GdOS (167µm) Spatial Frequency (mm -1 ) ModulationTransferFactor
  • 26. 26
  • 27. 27 200 µm 400 µm Scintillator / Flat PanelScintillator / Flat Panel DetectorDetector Effective Pixel Size -0.50 -0.25 0 0.25 0.50 Line Spread Function: Equivalent Aperture = 400µm 200 µm Pixel Size Distance (mm) Effective Pixel Size Actual Pixel Size CsI Light Spread
  • 28. 28 Scintillator / Flat Panel Detector  CsI - high x-ray absorption.  High DQE  Low scatter sensitivity.  Advantaged at high kV.  Dynamic / rapid imaging.  High manufacturing cost.  Dedicated TFT line required.  GdOS lower DQE.  CsI is hygroscopic. Strengths Weaknesses
  • 29. 29 Scintillator / Flat PanelScintillator / Flat Panel DetectorDetector
  • 30. 30 Photoconductor / Flat Panel Detector Drawing not to scale Programmable high-voltage power supply X-rays Gate pulse Charge amplifier Thin-film transistor Signal storage capacitor Glass substrate Charge collection electrode Electron blocking layer X-ray semiconductor Dielectric layer Top electrode Selenium E
  • 31. 31 Photoconductor / FlatPhotoconductor / Flat Panel DetectorPanel Detector Kodak DirectView Detector Magnified view of a portion of the TFTMagnified view of a portion of the TFT matrix. Arrow points to the center of amatrix. Arrow points to the center of a single 139 µm detector elementsingle 139 µm detector element DR9000
  • 32. 32 Why Selenium asWhy Selenium as Photoconductor?Photoconductor? ♦ Intrinsic high spatial resolution ♦ Demonstrated across the full medical diagnostic range (mammography through chest) ♦ Dynamic image capabilities . ♦ Long life ♦ Can be uniformly deposited over a large area ♦ Best advantage used in “charge accumulation mode”
  • 33. 33 Photoconductor / Flat PanelPhotoconductor / Flat Panel DetectorDetector -0.50 -0.25 0 0.25 0.50 Line Spread Function Equivalent Aperture = 139µm 139µm Pixel Size Distance (mm) 139µm 139µm Effective Pixel Size Actual Pixel Size
  • 34. 34 -0.50 -0.25 0 0.25 0.50 Distance (mm) Light spread and loss ofLight spread and loss of sharpnesssharpness
  • 35. 35 0 0.2 0.4 0.6 0.8 1.0 0 1 2 3 Film-Screen CCD Computed Radiography Direct Conversion Detector Indirect Conversion Detectors Spatial frequency (mm -1 ) ModulationTransferFactor
  • 36. 36 Photoconductor / Flat PanelPhotoconductor / Flat Panel DetectorDetector  Low manufacturingLow manufacturing cost.cost.  DQE > CR & CCDDQE > CR & CCD  Advantaged at lowAdvantaged at low kV (mammography)kV (mammography)  Se - low x-raySe - low x-ray absorptionabsorption  DQE < Indirect/CsIDQE < Indirect/CsI  High scatterHigh scatter sensitivitysensitivity  Image lag effects.Image lag effects.  Thermal sensitivity.Thermal sensitivity. Strengths Weaknesses
  • 37. 37
  • 38. There are two types of images, analog and digital, used in medical imaging.  Analog imagesAnalog images are the type of images that we, as humans, look at.  They include such things as TV images and all of our medical images displayed on various display devices, like computer monitors.  Digital imagesDigital images are recorded as numbers for the computer systems. 38
  • 39. 39
  • 40. 40
  • 41.  A digital image is represented in the imaging and computer system by numbers in the form of binary digits, called bits.  Then, multiple bits represent a Pixel.  Then matrix of pixels represent the Digital image. 41
  • 42. 42
  • 43.  The pixel bit depth is the number of bits that have been made available in the digital system to represent each pixel in the image. 43
  • 44. 44
  • 45.  When the pixel bit depth is increased to eight bits, a pixel can then have 256 different values (brightness levels, shades of gray, etc). 45
  • 46. 46
  • 47. 47
  • 48.  When an image is in digital form, it is actually blurred by the size of the pixel.This is because all anatomical detail within an individual pixel is "blurred together" and represented by one number.  The physical size of a pixel, relative to the anatomical objects, is the amount of blurring added to the imaging process by the digitizing of the image.  An image with small pixels (less blurring) displays much more detail than an image made up of larger pixels. 48
  • 49. 49
  • 50.  There are several digital processing methods that can be used to adjust the contrast characteristics of an image.  The two methods that we will consider here are: 1. Look Up Table (LUT) processing 2. Windowing 50
  • 51. 51
  • 52. 52
  • 53.  Many radiologists find value in having an . inverted (black bone) image in addition to the conventional (white bone) image at the time of viewing.  Some objects and structures might be more visible and easier to detect on the inverted image. 53
  • 54. 54
  • 55. 55
  • 56.  The process consist of two distinct steps. First, a blurred copy of the original image is produced.  by replacing each pixel value with the average of the pixel values in it's neighborhood.  This produces a "blurred mask" image 56
  • 57.  The final step is where the computer subtracts the blurred mask image (actually some fraction of it) from the original image.  This process increases the contrast of the details.  The result is that the contrast and visibility of the detail (small objects and structures) in enhanced. 57
  • 58. 58
  • 59. 59

Editor's Notes

  1. The signal profile and line-spread function show that greater image blur occurs with an indirect DR system The spreading of light in the imaging detector causes images to appear blurred. On the right the “point spread function” is illustrated. This shows that image information that should be recorded in the central pixel is spread into adjacent pixels. This is the source of the blur observed in the image on the lower left. Modulation transfer function is a well established way of characterizing this light spreading process. It is preferred to the “point spread function” because in linear systems the MTF of each component can simply be multiplied together to form the overall MTF. By contrast, the point spread functions would need to be convolved, a much more difficult mathematical operation. Image processing can restore the sharpness, but the image noise will also be enhanced (increased) in the process.
  2. The higher Nyquist frequency and MTF found with direct detector technology enhances visualization of fine detail and provides superior imaging performance.